1. Field of the Invention
The present invention relates to a linear motion rolling guide unit which is applied to sliding portions of machining tools and various processing equipment and which consists of a track rail with raceway grooves formed longitudinally extending on both side walls thereof, a casing saddling the track rail and having raceway grooves, and a number of rolling elements that roll between the facing raceway grooves.
2. Description of the Prior Art
In a conventional linear motion rolling guide unit, when a slider slides on a track rail, the seal between the slider and the track rail is provided by end seals mounted at both ends of the slider and an under seal mounted to the underside of the slider.
A linear motion rolling guide unit as shown in FIG. 8 has been disclosed. FIG. 8 is a perspective view showing one example of a conventional linear motion rolling guide unit. As shown in the figure, the linear motion rolling guide unit consists mainly of a track rail 1 with raceway surfaces 9 formed longitudinally extending on both side walls thereof and a slider 20 slidably mounted astride the track rail 1. The slider 20 is slidable relative to the track rail 1 and consists of a casing 2 having raceway surfaces 8 formed at positions facing the raceway surfaces 9, a number of rolling elements or balls 4, which are trapped between the opposing raceway surfaces 8, 9 to allow relative motion between the rail and the casing, and end caps 5 attached to the longitudinal ends of the casing 2.
The end cap 5 is fitted with an end seal 19 that provides a seal between the track rail 1 and the slider 20. The end cap 5 also has a grease nipple 18 for supplying lubricant to the sliding surface between the track rail 1 and the slider 20. To prevent the balls 4 from coming off the casing 2, a ball retaining band 17 is fitted into the casing 2 so as to enclose the balls 4. The casing 2 is provided with an under seal 3 to reliably prevent the balls 4 from coming off the casing 2 and to seal the casing 2, the longitudinal side walls 11 of the track rail 1 and the underside of the casing 2.
The slider 20 is mounted astride the rail 1 and is freely slidable on the rail 1 because of a number of balls 4 that circulate along the raceway surfaces 9 of the rail 1. That is, the balls 4 in a loaded region, i.e. those traveling on the raceway surafce 9 of the track rail 1, are led into a direction changing passage formed in the end cap 5 and further into a return passage 21 formed parallel to the raceway surface 8 in the upper part of the casing 2, so that the rolling elements 4 circulate in an endless raceway. As the balls 4 trapped between the raceway surface 8 formed in the slider 20 and the raceway surface 9 formed on the rail 1 roll under load, the slider 20 can freely move relative to the rail 1.
The under seal 3 is simple in shape and thus can be manufactured easily. However, the under seal 3 has the drawback of being easily deformed by external force when there are positioning errors of the casing 2 and the track rail 1 because it is formed of a thin plate. To describe in more detail, when the slider 20 slides on the track rail 1, any temperature variations and swelling by lubricant of the under seal 3 will deform the under seal 3 itself degrading its sealing performance. Further, the balls 4 may make contact with the under seal 3, increasing the sliding resistance.
The linear motion rolling guide unit as mentioned above is disclosed in the Japanese Patent Laid-Open No. 112021/1989. In another example the under seal is made up of a metal core member and a seal member fixed to the core member to keep the original shape of the under seal.
Generally, the linear motion rolling guide unit has a table securely mounted on a plurality of sliders (usually four) so that an equipment may be placed on the table. Example methods of mounting the table on the sliders are shown in FIGS. 6 and 7. FIG. 6 is a partially cutaway view showing one example method of mounting the table on the sliders; and FIG. 7 is a partially cutaway view showing another method of mounting the table on the sliders. In FIGS. 6 and 7 components having the same functions as those in FIG. 8 are given like reference numerals.
FIG. 6 shows one example of a four-raceway endless linear motion rolling guide unit. In this rolling guide unit, the slider 20 is shown to have mounting holes, through which bolts are screwed from under, with the table 6 mounted on the sliders 20. The track rail 1 is secured to the bed 22 by bolts. Normally, a pair of track rails 1 run parallel to each other, secured to the bed 22 by bolts. Two sliders 20 are slidably mounted on each track rail 1 and the table 6 is supported on four sliders 20 mounted on the two track rails 1. The casing 5 of the slider 20 has mounting holes 7, through which bolts are inserted from under. The table 6 is formed with threaded mounting holes 12. With the table 6 placed on the sliders 20, bolts 10 are inserted from under into the mounting holes 7 in the casing 2 and screwed into the threaded mounting holes 12 of the table 6 to fix the table 6 to the sliders 20.
FIG. 7 shows another example of the four-raceway endless linear motion rolling guide unit. In this example, a slider 20 is shown to have mounting holes through which bolts are inserted from above, with the table 6 mounted on the sliders. This example is similar to the one shown in FIG. 6 except for the table mounting method. The casing 2 of the slider 20 is formed with threaded mounting holes 13 on the upper side. The table 6 is formed with mounting holes through which bolts are inserted from above. With the table 6 mounted on the sliders 20, bolts 10 are inserted from above into the mounting holes 14 in the table and screwed into the threaded mounting holes 13 in the casing, thus securing the table 6 to the sliders 20.
Let us consider a case where the under seal 3 is made up of a metal core member and a plastic sealing member fixed to the core member. In the linear motion rolling guide unit of FIG. 6, when the under seal 3 is fixed to the casing 2, it is necessary to form through-holes in the under seal 3 through which to insert the bolts 10 because the casings 2 are secured to the table 6 by bolts 10. On the other hand, in the linear motion rolling guide unit as shown in FIG. 7 where the table 6 is secured to the casings 2 by bolts 10, since the bolts 10 are not passed through the under seal 3, it is not necessary to form the through-holes in the under seal 3 for the bolts 10.
That is, in the linear motion rolling guide unit of FIG. 6, the through-holes for the bolts 10 must be formed in the under seal 3. In the linear motion rolling guide unit of FIG. 7, on the other hand, there is no need to form through-holes in the under seal 3. It should be noted, however, that the under seal 3 is required to seal the gap between the track rail 1 and the slider 20 to prevent ingress of dirt, water and other foreign matters. Hence, it is desired that the under seal 3 is not formed with through-holes. To solve this problem, it is necessary to form two kinds of under seal 3.